There exists a known seat position control device, which is adapted to a vehicle and the like and which automatically adjusts a position of a seat to a desired seat position (i.e. a seat position) memorized in a memory by operating a switch, even after an occupant changes the seat position. In order to adjust the seat position, a slide motor for moving an entire seat forward and rearward relative to a vehicle body, a reclining motor for changing an inclination of a seat-back, and the like are provided at the seat. By driving the above-mentioned motors by a switch operation, the seat is adjustable to any desired position. The seat position control devices for adjusting the seat position disclosed in, for example, JP2000-250629A and JP2002-325475A, detect a ripple component included in a motor current of a motor for driving the seat as a ripple pulse synchronized with a rotation of the motor via a pulse generating circuit having a differentiating circuit, without using a rotational sensor for detecting a rotational position of the motor, and then, the seat position control device executes a position control of the seat on the basis of the detected ripple pulse.
In the case where the position control of the seat and the like is executed by using the ripple pulse synchronized with the rotation of the motor, without using the rotational sensor for detecting the rotational position of the motor, an amount of the motor being actuated (i.e. an amount of actuation) due to an inertia generated after a motor output is stopped is not detectable because the ripple pulse is generated only while the motor is actuated, on the other hand, the ripple pulse is not generated after the motor output is stopped. Therefore, a state memorizing device, disclosed in JP2000-250629A, estimates the actuation amount of the motor generated after the motor output is stopped on the basis of a rotational amount of the motor while being actuated. Then, the state memorizing device, disclosed in JP2000-250629A, corrects a positional information, thereby obtaining a position of the seat. In order to estimate the rotational amount of the motor, the state memorizing device preliminarily stores therein a correction map, which specifies a relationship among an actuation portion, voltage, a pulse period and the like.
Further, in the case where the position control of the seat and the like is executed by using a motor ripple pulse synchronized with the rotation of the motor, without using the rotational sensor for detecting the rotational position of the motor, the rotational position of the motor may not be detected especially in a case where the motor rotates at a very low speed since when the motor is started, because an accurate ripple pulse is not generated when the motor is rotated at the very low speed (a very low speed rotation). Therefore, a control device for the motor disclosed in JP2002-325475A executes a motor control in consideration of the very low speed rotation by detecting the very low speed rotation of the motor when being started by using a motor current of when the motor is started and a motor current of when the motor is normally driven.
The state memorizing device, disclosed in JP2000-250629A, estimates the actuation amount of the motor generated after the motor output is stopped. However, in the case where the motor rotates at the very low speed since when the motor is started, the actuation amount is not accurately estimable. Further, the control device for the motor, disclosed in JP2002-325475A, detects the very low speed rotation of the motor of when being started on the basis of the current flowing through the motor when the motor is started and the current flowing through the motor when the motor is normally driven, and then, the control device estimates the rotational position of the motor. Therefore, the output of the motor is easily stopped. However, in a case where the output of the motor is stopped, the very low speed rotation of the motor is not detectable.
When the output of the motor is stopped in a case where the motor, which is provided at, for example, a seat for a vehicle, a sunroof and the like, is controlled so as to be actuated towards a mechanical end point direction while the seat, the sunroof and the like (the movable member) are positioned at corresponding mechanical end points (at an end point within a range of movement), in other words, in a case where the motor is driven at the very low speed (motor lock), the movable member may be moved opposite from an actuation direction because of backlash, deterioration with age of a gear and the like for changing a position of the movable member or because of deflection and the like of a impact absorbing member provided at the mechanical end point for absorbing an impact generated when a portion for changing the position of the vehicle, the sunroof and the like for the vehicle (i.e. a changing member) contacts the mechanical end point. Such movement in the reverse direction results in a displacement of the memorized position in the control.
If the changing member is further actuated in the mechanical end point direction than the mechanical end point for the deflection amount and an absorbing amount of the impact absorbing member, an actuation amount of the changing member being actuated further in the mechanical end point than the mechanical end point is measured in a case where the current is supplied to a controlling portion. However, if the current supply to the controlling portion is cut, the moving amount of the changing portion moved afterwards by a biasing force acting on the impact absorbing member is not detectable. Accordingly, a displacement occurs between an actual position of the changing member and the position memorized by the controlling portion. Such displacement gradually increases by accumulation of the displacement occurring each time when the above-described phenomenon occurs. Therefore, even if a user operates a switch and the like to retrieve the seat, the sunroof and the like for the vehicle to the preliminarily memorized position, the seat, the son roof and the like may be moved to a position displaced from the position the user desires.
A need thus exists to provide a state memorizing device for a movable member which is not susceptible to the drawback mentioned above.